We studied the change in the 3d-shell configurations of Fe in B-doped Si under illumination by electron spin resonance (ESR) measurement. ESR signals originating from Fe-i(+)(3d(7)) and Fe-i(0)(3d(8)) were observed in Fe- and B-doped Si. The ESR signal of Fe-i(+)(3d(7)) disappeared and the signal intensity of Fe-i(0)(3d(8)) increased under illumination. These changes of the ESR signals under illumination were caused by the change in the charge state from Fe-i(+)(3d(7)) to Fe-i(0)(3d(8)) due to the capture of an electron. Subsequently, the process of recovery from Fe-i(0)(3d(8)) to Fe-i(+)(3d(7)) due to the capture of a hole was observed after the light was turned off. We found that the relaxation time from Fe-i(0)(3d(8)) to Fe-i(+)(3d(7)) was approximately 30 s at 8 K. This was much longer than the lifetime of a free hole.